The following invention relates to the use of chlorinated benzene diamine. Specifically, the present invention relates to the curing of epoxy resins, for example, diglycidyl ether of bisphenol A and its homologs by the use of these compounds.
The cross-linking of epoxy resins, which is generally known as curing, is accomplished by the reaction of epoxy groups with active hydrogen-containing acids and bases. These hydrogen-containing acids and bases are generally provided by two classes of curing agents. These are amines which act as chain extenders, and acid curing agents which may act as esterification and etherification agents.
The use of amines as curing agents could include both primary and secondary aliphatic and aromatic amines. Aliphatic or aromatic tertiary amines have not been found useful as curing agents because they do not contain acidic hydrogen atoms and will therefore produce only homopolymerization.
The aliphatic and aromatic primary and secondary amines have been preferred to the acid curing agents, and specifically to the acid anhydrides for higher temperature work from the standpoint of chemical resistance. See, for example, Epoxy Resins H. Lee and K. Neville, McGraw-Hill, N.Y., 1957, page 100.
Because they provide a significant increase in the heat distortion temperature of the cured resin system, the use of aromatic amines and specifically aromatic diamines should be preferred over the aliphatic amines. This is because the stable benzene ring is tightly cross-linked into the cured structure. And if a diamine is used, it also may become a part of the epoxy backbone. As a result, certain aromatic diamines provide heat distortion temperatures 40.degree.-60.degree. C. higher than those obtained with even the most thoroughly post-cured aliphatic amines. However, with the exception of m-phenylene diamine, 4,4' methylene dianiline, and diamino diphenyl sulfone, other aromatic diamines have not shown any economic advantage over primary and secondary aliphatic amines. Their use has also been limited by their relatively high toxicity. See HANDBOOK OF EPOXY RESINS, H. Lee and K. Neville, McGraw-Hill, N.Y., 1967, pages 8-10 to 8-12.